VARIATIONS ON MENDEL S LAWS

Transcription

1 VAIATIONS ON MENDEL S LAWS Incomplete Dominance in Plants and People 2 Some pattens of genetic inheitance ae not explained b Mendel s laws. In incomplete dominance, F hbids have an appeaance between the phenotpes of the two paents. 203 Peason Education, Inc. 203 Peason Education, Inc. Figue 9.- P Geneation 3 Figue 9.-2 P Geneation ed White ed White F Geneation Pink 2 2

2 Figue 9.-3 P Geneation ed White 5 Incomplete Dominance in Plants and People Hpecholesteolemia F Geneation 2 2 Pink is a human tait that is an example of incomplete dominance and is chaacteized b dangeousl high levels of cholesteol in the blood. F 2 Geneation Spem Peason Education, Inc. Incomplete Dominance in Plants and People 7 Figue 9.9 In hpecholesteolemia, heteozgotes have blood cholesteol levels about twice nomal, and homozgotes have about five times the nomal amount of blood cholesteol and ma have heat attacks as eal as age 2. GENOTPE PHENOTPE LDL ecepto Homozgous fo abilit to make LDL eceptos LDL HH Hh hh Heteozgous Cell Nomal Mild disease Homozgous fo inabilit to make LDL eceptos Sevee disease 203 Peason Education, Inc.

3 ABO Blood Goups: An Example of Multiple Alleles and Codominance 9 ABO Blood Goups: An Example of Multiple Alleles and Codominance 70 The ABO blood goups in humans ae an example of multiple alleles. The immune sstem poduces blood poteins called antibodies that bind specificall to foeign cabohdates. If a dono s blood cells have a cabohdate (A o B) that is foeign to the ecipient, the blood cells ma clump togethe, potentiall killing the ecipient. The clumping eaction is the basis of a bloodtping lab test. The human blood tpe alleles I A and I B ae codominant, meaning that both alleles ae expessed in heteozgous individuals who have tpe AB blood. 203 Peason Education, Inc. 203 Peason Education, Inc. Figue 9.20a 7 Figue 9.20b 72 Blood Goup (Phenotpe) Genotpes ed Blood Cells Antibodies Pesent in Blood Blood Goup (Phenotpe) eactions When Blood fom Goups Below Is Mixed with Antibodies fom Goups at Left O A B AB A I A I A o I A i Cabohdate A Anti-B A B I B I B o I B i Cabohdate B Anti-A B AB I A I B AB O ii Anti-A Anti-B O

4 Pleiotop and Sickle-Cell Disease 73 Figue 9.2 Individual homozgous fo sickle-cell allele 74 Pleiotop is when one gene influences seveal chaactes. Sickle-cell (abnomal) hemoglobin Sickle-cell disease exhibits pleiotop, esults in abnomal hemoglobin poteins, and causes disk-shaped ed blood cells to defom into a sickle shape with jagged edges. Abnomal hemoglobin cstallizes into long flexible chains, causing ed blood cells to become sickle-shaped. Coloized SEM 203 Peason Education, Inc. Sickled cells can lead to a cascade of smptoms, such as weakness, pain, ogan damage, and paalsis. Polgenic Inheitance Polgenic inheitance is the additive effects of two o moe genes on a single phenotpe. 75 Figue 9. P Geneation F Geneation aabbcc (ve shot) AaBbCc (medium height) AABBCC (ve tall) AaBbCc (medium height) = shot allele = tall allele 7 F 2 Geneation Spem Faction of population 20 5 Ve shot Adult height Ve tall Peason Education, Inc.

5 Figue 9.a 77 Figue 9.b 7 P Geneation F Geneation aabbcc (ve shot) AABBCC (ve tall) = shot allele = tall allele F 2 Geneation AaBbCc (medium height) AaBbCc (medium height) = shot allele = tall allele Figue 9.c 79 The ole of Envionment 0 Faction of population 20 5 Man human chaactes esult fom a combination of heedit and envionment. Onl genetic influences ae inheited. Ve shot Adult height Ve tall 203 Peason Education, Inc.

6 Figue 9.23 THE CHOMOSOMAL BASIS OF INHEITANCE The chomosome theo of inheitance states that genes ae located at specific positions (loci) on chomosomes and the behavio of chomosomes duing meiosis and fetilization accounts fo inheitance pattens Peason Education, Inc. THE CHOMOSOMAL BASIS OF INHEITANCE It is chomosomes that undego segegation and independent assotment duing meiosis and account fo Mendel s laws. 3 Figue 9.24 P Geneation F Geneation ound-ellow seeds () Law of Segegation: Follow the long chomosomes (caing and ) taking eithe the left o ight banch. The and alleles segegate in anaphase I of meiosis. Onl one long chomosome ends up in each gamete. MEIOSIS FETILIZATION MEIOSIS Metaphase I (altenative aangements) Metaphase II All ound-ellow seeds () Winkled-geen seeds () Law of Independent Assotment: Follow both the long and the shot chomosomes. The ae aanged in eithe of two equall likel was at metaphase I. The sot independentl, giving fou gamete tpes Peason Education, Inc. Fetilization ecombines the and alleles at andom. F 2 Geneation FETILIZATION AMONG THE F PLANTS 9 : 3 : 3 : Fetilization esults in the 9:3:3: phenotpic atio in the F 2 geneation.

7 Linked Genes 5 Figue Dihbid testcoss Linked genes Ga bod, long wings (wild-tpe) Black bod, shot wings (mutant) ae located close togethe on a chomosome and GgLl ggll tend to be inheited togethe. Thomas Hunt Mogan used the fuit fl Dosophila melanogaste and detemined that some genes wee linked based on the inheitance pattens of thei taits. 203 Peason Education, Inc. Figue Dihbid testcoss 7 Genetic ecombination: Cossing Ove Ga bod, long wings (wild-tpe) Black bod, shot wings (mutant) Cossing ove can GgLl ggll sepaate linked alleles, poduce gametes with ecombinant gametes, and esults Offsping poduce offsping with ecombinant phenotpes. Ga-long GgLl Black-shot ggll Ga-shot Ggll Black-long ggll The pecentage of ecombinant offsping among the total is called the ecombination fequenc Paental phenotpes 3% ecombinant phenotpes 7% 203 Peason Education, Inc.

8 Figue Figue GgLl (female) G L ggll (male) A B a b COSSING OVE A B G L G l g L a b Pai of homologous chomosomes Cossing ove Paental gametes A b a B ecombinant gametes Paental gametes ecombinant gametes FETILIZATION Offsping Spem G L Paental G l g L ecombinant Figue 9.27a 9 Figue 9.27b 92 G L G l g L GgLl (female) G L ggll (male) Paental gametes ecombinant gametes Spem FETILIZATION COSSING OVE Offsping G L G l g L Paental gametes ecombinant gametes Spem G L Paental G l ecombinant g L

9 Linkage Maps 93 Figue Eal studies of cossing ove wee pefomed using the fuit fl Dosophila melanogaste. Alfed H. Stutevant, a student of Mogan, Chomosome g c l developed a method fo mapping the elative gene locations, 7% which esulted in the ceation of linkage maps. 9% ecombination fequencies 9.5% 203 Peason Education, Inc. SEX CHOMOSOMES AND SEX-LINKED GENES 95 Figue Sex chomosomes influence the inheitance of cetain taits. Fo example, humans that have a pai of sex chomosomes designated X X Somatic cells XX X and ae male o X and X ae female. Coloized SEM X X Spem Egg XX Offsping X 203 Peason Education, Inc.

10 Figue 9.29a 97 Figue 9.29b 9 X Somatic cells XX X X X Spem Egg XX Offsping X Coloized SEM Sex Detemination in Humans 99 Sex-Linked Genes 00 Neal all mammals have a pai of sex chomosomes designated X and. s have an X and. s have XX. An gene located on a sex chomosome is called a sex-linked gene. Most sex-linked genes ae found on the X chomosome. ed-geen coloblindness is a common human sex-linked disode and caused b a malfunction of light-sensitive cells in the ees. 203 Peason Education, Inc. 203 Peason Education, Inc.

11 Figue Figue X N X N X n X N X n X N X N X n X n X n Spem X N Spem X n Spem X N X N X n X N X N X N X N X N X N X N X n X N X N X N X n X N X n X N X n X n X n X n X n X n (a) Nomal female coloblind male (b) Caie female nomal male (c) Caie female coloblind male Ke Unaffected individual Caie Coloblind individual